1. Technical Field
The disclosure relates to a flat speaker having a moisture blocking characteristic.
2. Background Art
Vision and audition are the most direct sensory responses of human beings. Thus, scientists have been dedicated to developing various renewable vision and audition related systems. Moving coil speaker is still the major product in the market among all the existing renewable speakers. However, along with people's increasing demand to high quality sensory enjoyment and the ever-decreasing sizes of 3C products (Computer, Communication, and Consumer Electronics), speakers which have low power consumption, light weights, and small sizes and are designed according to human factors engineering are to be developed and broadly applied in the near future.
The existing speakers can be categorized into direct and indirect types according to their radiation patterns or can be categorized into moving coil speaker, piezoelectric speaker, and electrostatic speaker according to the driving patterns thereof. The moving coil speaker is currently the most commonly used and most mature product. However, a moving coil speaker cannot be compressed due to the physical structure thereof. Accordingly, moving coil speaker is not suitable for 3C products and home entertainment systems which have their sizes reduced constantly.
A piezoelectric speaker pushes a membrane to produce sounds based on the piezoelectric effect of an electrical material (i.e., the material is deformed when an electric field is supplied thereon). A piezoelectric speaker has a compressed and small structure. Electrostatic speaker is a hi-end earphone or speaker in the current market. According to the operation principle of a conventional electrostatic speaker, a conductive membrane is disposed between two open-hole electrical backplates to form a capacitor. An electric field is produced by supplying a DC bias to the membrane and an AC voltage to the two electrical backplates. The conductive membrane is driven by the electrostatic force generated by the electric field to vibrate and accordingly produce audio. The conventional electrostatic speaker needs a bias of up to hundreds or even thousands voltages, and accordingly a high-cost and bulky amplifier has to be used which makes the conventional electrostatic speaker difficult to popularize.
Audio is a major element in the future applications of flexible electronics. However, flexible electronics has to have the characteristics of softness, thinness, low driving voltage, and high flexibility. Thus, how to fabricate elements having the characteristics of flexible electronics has become a major subject.
Currently, the manufacture of speakers still applies the design production method as that for a single unit as illustrated in U.S. Pat. No. 3,894,199.
As for the electrostatic speaker, for example, in U.S. Pat. No. 3,894,199, an electro-acoustic transducer structure is mainly provided, as shown in FIG. 1. The structure includes two fixed electrode structures 110 and 120 placed on two sides. The fixed electrode structures 110 and 120 have a plurality of pores for scattering the sounds generated. A vibrating film 130 is disposed between the fixed electrode structures 110 and 120. A fixing structure 140 is made of an insulation material, and used to fix the fixed electrode structures 110 and 120 and the vibrating film 130. The fixed electrode structures 110 and 120 are respectively connected to an AC source 160 through a transformer 150. When an AC signal is transmitted to the fixed electrode structures 110 and 120, a potential is alternately changed to enable the vibrating film 130 to generate vibration due to the potential difference on two sides thereof, and thereby generating corresponding sound. However, the above configuration needs to enhance the sound-pressure output, so an additional power element is required to work together with the driving process. In this manner, the apparatus not only has a large volume, but more elements are used, and the cost is relatively high. In addition, the fixing structure 140 must fix the fixed electrode structures 110 and 120 and the vibrating film 130, so the electro-acoustic transducer structure cannot achieve the flexible characteristics.